Between 3 billion and 5 billion birds formed feathered tempests that blackened the skies and shocked early colonists with their numbers.

Passenger pigeons accounted for a quarter of all birds north of Mexico, and it might well have been the most abundant bird on Earth.

Naturalist John James Audubon once described a pigeon flight that he observed along the banks of the Ohio River in 1813.

The flocks passed for three days and dominated the landscape. Audubon tried to estimate the numbers of pigeons and arrived at a figure of 1.1 billion birds.

A flock over Columbus in 1855 was said to have taken all day to pass. The birds blotted out the sun, spooked horses and scared startled citizens indoors. The feathered storm whitened the landscape with droppings.

Passenger pigeons fed primarily on acorns and other tree mast, and wandered far and wide in search of food. Massive nesting colonies formed in favored locations, and the largest on record covered an area of 850 square miles in central Wisconsin. As a point of comparison, Franklin County, Ohio, is 543 square miles.

The pigeons made an impression on settlers: Scores of towns and landmarks were named for them. Pigeon Creek near Akron, Pigeon Forge in Tennessee and the Pigeon River in Michigan serve as epitaphs.

By the late 1800s, ornithologists were lamenting tremendous declines in pigeon numbers. The birds were no match for people armed with guns, and they proved to be easy targets. Mass slaughters were common.

Many pigeons were eaten, but huge numbers were shot for “sport,” their bodies left to rot. Passenger pigeons were birds of the forests primeval, and as settlers cleared woodlands with alarming rapidity, pigeon habitat quickly dwindled.

The passenger pigeon, in spite of its staggering numbers, had no chance against the 19th-century explosion of Homo sapiens in North America.

The last wild passenger pigeon is thought to have been shot on March 24, 1900, in Pike County, Ohio. Captives still existed in zoos, and the last of these, Martha, died on Sept. 1, 1914, in the Cincinnati Zoo.

No one who witnessed the massive flocks just a century before would have ever predicted the bird’s extinction.

The pigeon is a tragic lesson not to be forgotten.

At 11 a.m. Sept. 6, a program about the passenger pigeon will be presented at Green Lawn Cemetery, 1000 Greenlawn Ave. A monument to the pigeon will also be unveiled. The cemetery’s ancient oaks undoubtedly once hosted passenger pigeons.

On Friday and Saturday, the Cincinnati Zoo will host a passenger pigeon symposium. The keynote speaker is Joel Greenberg, author of A Feathered River Across the Sky: The Passenger Pigeon’s Flight to Extinction — the best book to date about the bird.